This invention relates generally to voltage control of an electrical power bus, and more particularly the invention relates to bus voltage control when a variable load is connected to the bus.
In a number of applications, including communications satellites, a DC power bus is provided to power electrical circuitry. Bus capacitors are charged to a desired voltage by a battery and by solar cells, for example, to maintain the requisite voltage.
The bus capacitors must be periodically recharged to maintain a desired voltage range. Heretofore, bus voltage control circuitry has employed linear feedback to control the duty cycle, or on and off cycle, of energy pulses in response to varying bus voltage. See U.S. Pat. Nos. 6,275,018 and 6,304,473, for example. This can include variable pulse on and off times, and variable repetition times. As described in the '018 patent, control methodologies or strategies may be broadly classified into two categories including those with control frame and those without a control frame. To regulate an output voltage, a controller may be coupled to a signal proportional to the output voltage so that an error signal representing the difference between the current value of the output voltage and a desired level of output voltage can be generated. The controller then regulates the output voltage according to the error signal. This regulation is accomplished by controlling a power switch and a free-running oscillator for producing a drive signal to cycle the power switch on and off, wherein the power switch when coupled to a power source and cycled on and off defines a pulse of power to the load, and a controller regulates an output voltage at the load by varying the number of pulses of power occurring at the load over time.
The control frames can be of fixed length or variable length. Within a fixed control frame, the on and off states can define a pulse train of pulses having a duty cycle defined by the length of the pulse train with respect to the fixed frame control period wherein the controller varies the duty cycle to regulate the output voltage. In another embodiment, the on and off stage of the switch control combination are varied to remove randomly a necessary number of pulses from the pulse train within a fixed control frame. In another embodiment, the removal of a necessary number of pulses can occur at harmonics of the frequency defined by the fixed control frame.
If the control frame is variable, a number of alternate control strategies can be used including having the on state of the switch control combination occur within a fixed period in a variable control frame thereby resulting in a variable period of the off state. Alternatively, the off state of the switch control combination can occur within a fixed period with a variable control frame, resulting in a variable period for the on state. In yet another alternate embodiment, the periods for the on and off states can both be variable within a variable control period.
In an embodiment where there is no control frame, a technique called “prompt gating” is proposed. In these embodiments the controller determines, on a pulse by pulse basis, whether a pulse of power occurs at the output. All of these embodiments are complex in energy pulse control.
The present invention is directed to a power bus controller with simplicity of control.